On Thu, 23 Jul 2026 10:36:32 -0700 Stanislav Kinsburskii
<[email protected]> wrote:
> This series extends the HMM framework to support userfaultfd-backed memory
> by allowing the mmap read lock to be dropped during hmm_range_fault().
>
Thanks, I've updated mm.git to this version.
AI review suggests there may be some problems. Sorry, I don't recall if
these were considered in previous versions of the patchset:
https://sashiko.dev/#/patchset/[email protected]
>
> Changes in v11:
> - Reject unstable address spaces in hmm_range_fault_unlocked_timeout()
> after taking mmap_lock and before walking page tables.
> - Compute the remaining HMM timeout budget before the time_after_eq()
> check in drm_gpusvm_get_pages() to make sure it can't result in zero
> and lead to infinite HMM range faulting loop.
Here's how v11 altered mm.git:
drivers/gpu/drm/drm_gpusvm.c | 4 ++--
mm/hmm.c | 6 ++++++
2 files changed, 8 insertions(+), 2 deletions(-)
--- a/drivers/gpu/drm/drm_gpusvm.c~b
+++ a/drivers/gpu/drm/drm_gpusvm.c
@@ -1422,11 +1422,11 @@ int drm_gpusvm_get_pages(struct drm_gpus
struct dma_iova_state *state = &svm_pages->state;
retry:
+ remaining = timeout - jiffies;
+
if (time_after_eq(jiffies, timeout))
return -EBUSY;
- remaining = timeout - jiffies;
-
hmm_range.notifier_seq = mmu_interval_read_begin(notifier);
if (drm_gpusvm_pages_valid_unlocked(gpusvm, svm_pages))
goto set_seqno;
--- a/mm/hmm.c~b
+++ a/mm/hmm.c
@@ -17,6 +17,7 @@
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/mmzone.h>
+#include <linux/oom.h>
#include <linux/pagemap.h>
#include <linux/leafops.h>
#include <linux/hugetlb.h>
@@ -806,6 +807,11 @@ int hmm_range_fault_unlocked_timeout(str
if (ret)
return ret;
+ if (check_stable_address_space(mm)) {
+ mmap_read_unlock(mm);
+ return -EFAULT;
+ }
+
if (timeout && time_after(jiffies, deadline)) {
mmap_read_unlock(mm);
return -EBUSY;
_
